Where The Warmth Is

I got to thinking about the “hiatus” in warming in the 21st Century, and I realized that the CERES satellite dataset covers the period since the year 2000. So I’ve graphed up a few views of the temperature changes over the period of the CERES record, which at present is May 2000 to February 2017. No great insights, just a good overview and some interesting findings.

First, here are the raw CERES global average surface temperature data, the seasonal variations, and the anomaly that remains after removing the seasonal variations.

Figure 1. Seasonal decomposition of the CERES surface temperature data. Statistical results (bottom line) are adjusted for autocorrelation using the method of Koutsoyiannis.

So … what are we looking at? The top panel shows the raw data, the actual temperature variations. The middle panel shows the repeating seasonal variations. The bottom panel shows the “residual anomaly”, the variations that remain once we’ve removed the repeating seasonal component of the signal.

The bottom panel, the residual anomaly, is the panel of interest. You can see how little the temperature has varied over the seventeen years of record. The El Nino of 2016-2017 is quite visible … but other than that there isn’t much happening.

There is one thing that is interesting about the residual … other than warming as a result of the 2016-2017 El Nino, the temperature anomaly only varied by about ± 0.2°C. Among other places, I’ve discussed what I see as the reason for this amazing stability in a post called Emergent Climate Phenomena.

The next question of interest to me is, where is the temperature changing, and by how much? Here is a Pacific and an Atlantic centered view of the warming trends recorded by CERES, in degrees C per decade.

Figure 2. Temperature trends around the globe.

So … what is of note in these global maps? Well, both the poles are unusual. The area around Antarctica is cooling strongly, and the Arctic is warming. Presumably, this is why we’re getting less sea ice in the North and more sea ice in the South. It also affects the hemispheric averages, with the Northern Hemisphere warming and the Southern Hemisphere basically unchanging. Figure 3 shows the average decadal temperature trends by latitude band.

Figure 3. Average decadal temperature trends by latitude band.

As you can see, the only parts of the planet where the temperature is changing much are the Southern Ocean around Antarctica, and the area above the Arctic Circle.

Next, in Figure 2 you can see that the North Atlantic is generally cooling. On the other hand, the Pacific is mixed, with areas of slight cooling and other areas of slight warming. Go figure.

On land, northern Russia, parts of the Sahel, the Gobi, and western Australia are warming. On the other hand, the upper Amazon is cooling strongly. So it looks like some (but not all) deserts are warming, and some (but not all) tropical forests are cooling … why?

I haven’t a clue. In my opinion, the most important words that anyone studying the climate can learn to say are “I don’t know.”

At the end of the story, I’m left with my usual amazement at the stability of the system. Despite being controlled by things as evanescent as winds, waves, and clouds, the temperature anomaly doesn’t vary more than about two-tenths of a degree. Nor is this due to “thermal inertia” as many people claim. Look again at Figure 1—the temperature changes by four degrees C peak to peak in the course of a single year, and changes by a degree and a quarter C in a single month, but the anomaly barely budges. To me, this is clear evidence of strong thermoregulatory systems, but of course, YMMV …